Long Term Evolution-Advanced (Long Term Evolution-Advanced, “LTE-A” for short) is a further evolved and enhanced 3rd Generation Partnership Project (3rd Generation Partnership Project, “3GPP” for short) LTE system. To meet the requirement of the International Telecommunication Union on the peak data rate of 4th generation communications technologies, the carrier aggregation (Carrier Aggregation, “CA” for short) technology, also called the spectrum aggregation (Spectrum Aggregation) technology or the bandwidth extension (Bandwidth Extension) technology, is introduced into the LTE-A system. In the carrier aggregation technology, spectrums of two or more component carriers (Component Carrier, “CC” for short) are aggregated to obtain a wider transmission bandwidth, the spectrums of the component carriers may be adjacent consecutive spectrums, or non-adjacent spectrums at a same frequency band, or even nonconsecutive spectrums at different frequency bands. In an LTE Release 8 or 9 (Release 8 or 9, “Rel-8/9” for short) system, a user equipment (User Equipment, “UE” for short) is only capable of accessing one of the component carriers to receive and transmit data; however, in the LTE-A system, a user equipment can simultaneously access multiple component carriers to receive and transmit data according to its capability and service requirement.
To support technologies, such as dynamic scheduling and downlink multiple input multiple output (Multiple Input Multiple Output, “MIMO” for short) transmission, the user equipment needs to feed back channel state information (Channel State Information, “CSI” for short) to a base station (Evolved NodeB, “eNB” for short). Because the carrier aggregation technology is introduced into the LTE-A system, channel state information of each component carrier needs to be fed back in an uplink direction when the user equipment simultaneously accesses multiple component carriers to receive downlink data. That is, in a scenario of carrier aggregation in the LTE-A system, a case where channel state information of multiple downlink carriers needs to be transmitted on one subframe may occur.
Therefore, a technical solution is required to transmit channel state information from different downlink carriers on a same sub-frame.